Grushow is leaving to form his own production company based at 20th Century Fox, called Phase Two, it was announced Monday.

"This was a very complicated decision for me to make," Grushow said in a statement. He concluded it was better to exercise a production option in his contract rather than sign another executive agreement, he said.

Fox TV started the season with an unprecedented bang, topping the prime-time ratings for three weeks in a row.

But a ripple effect for regular series didn't follow. The network was hit by the failure of a second edition of the reality show "Joe Millionaire," and returning Fox shows, including hits such as "24," also saw a drop in ratings.